Method for producing a complex nonwoven fabric and resulting novel fabric

ABSTRACT

The invention concerns a method for producing a complex nonwoven fabric which consists in continuously producing a complex wherein a first web of a cellulosic fibres ( 4 ) is continuously sandwiched between two webs of spunbonded filaments ( 2, 7 ), and which consists in: producing a first web of spunbonded filaments ( 2 ), the bundle of extruded and drawn filaments being received on a mobile conveyor belt ( 3 ) in the form of a non-bonded lap; depositing on said web  92 ) by airlaid process a second web of cellulosic fibres ( 4 ); depositing on the textile web ( 4 ) a second web ( 7 ) of non-bonded continuous filaments; transferring the resulting complex onto an installation ( 9 ) for water-jet bonding and hydro-entanglement consolidation; and in drying the nonwoven mixed product and then recuperating it, for example in the form of a cloth wind-up ( 18 ).

TECHNICAL FIELD

[0001] For decades, it has been proposed to replace conventional textilewebs (wovens and knits) with structures called “nonwovens”.

[0002] In general, such nonwoven structures can be classified in threebroad categories, resulting from their actual manufacturing process,namely nonwovens produced by a so-called “dry process”, these beingformed by carding and/or the airlaid technique, nonwovens obtained bythe “melt route”, which technique is usually referred to by theexpression “spunbond”, and the technique called “wet process” derivedfrom papermaking techniques.

[0003] Moreover, it has been known for a very long time that it ispossible to adapt the final properties of the product obtained byproducing mixtures of materials, for example by combining together websconsisting of fibers of different type, for example natural, artificialor synthetic fibers.

[0004] The invention provides a novel method making it possible toproduce such a type of nonwoven article consisting of a mixture offibers of different type, which nonwoven will, in the rest of thedescription, be referred to by the expression “hybrid nonwoven” or“composite nonwoven”.

PRIOR ART

[0005] Very many proposals have been made hitherto for producing hybridor composite nonwovens by combining together webs of artificial orsynthetic fibers with a web of cellulosic fibers. The variousconstituents may be combined in various ways, for example by means ofbonding techniques—mechanical needle bonding or hydro-entanglement—thelatter technique, known for a very long time, being described forexample in U.S. Pat. No. 3,508,308. In particular, this documentdescribes the production of hybrid webs produced by the airlaidtechnique by intimately mixing fibers, for example mixing synthetic(polyester or acrylic) fibers with rayon fibers (see examples 10 and11). It also describes (see examples 12 and 13) the production ofcomplexes having a central ply consisting of continuous filaments andtwo outer plies based on fibers, especially polyester fibers, which aredistributed by the airlaid technique, the various plies being bondedtogether by the action of fluid jets.

[0006] It has also been proposed, as indicated in EP 423 619, to produceabsorbent fabrics by combining, again by means of water jets, a webconsisting of continuous filaments with a web consisting of a mixture ofcellulosic fibers, especially wood fibers.

[0007] Finally, it is known to produce nonwovens by sandwiching a lap offibers between two webs of continuous filaments already consolidated byhot calendering, the final bonding of the various plies also beingprovided-by the action of water jets.

[0008] The latter relatively simple processing technique has many majordrawbacks, namely:

[0009] the fact that the webs of continuous (spunbond) filaments havealready been consolidated by a calendering heat treatment preventsintimate mixing of these filaments with the wood fibers of the airlaidweb, which reduces the absorptivity of the complex and also results inthe formation of a product which is rough and lacking in flexibility;

[0010] moreover, it is necessary, in order to ensure satisfactorycohesion between the plies and prevent delamination of the complex, touse, during the water-jet consolidation phase, very high fluidvelocities, since the calendering points of the spunbond webs preventany mobility of the synthetic filaments; these high water-jet velocitiesincur an extra energy consumption cost and a greater loss of cellulosicfiber;

[0011] the points of bonding between the filaments obtained bycalendering may represent up to 20 to 25% of the area of thespunbond-based webs and therefore constitute an equivalent amount ofobstacles to the passage of the water jets;

[0012] finally, the fact that the continuous filaments of the webscannot move makes the material very stiff, it losing its textileproperties and being more like a paper than a true textile.

SUMMARY OF THE INVENTION

[0013] An improved method has now been found, and it is this which formsthe subject of the present invention, which allows the continuousproduction of perfectly bonded hybrid nonwovens exhibiting highmechanical properties while retaining the appearance, handle andflexibility of a conventional textile, such as a woven.

[0014] Such a problem is solved by combining, in a very precise way,techniques of the prior art used continuously and under very preciseconditions, namely:

[0015] the techniques for producing nonwoven webs made from shortfibers, which are distributed by the airlaid technique;

[0016] the techniques for producing spunbond webs; and

[0017] consolidation of the complex formed by the action of water jets.

[0018] In general, the method according to the invention consists incontinuously producing a complex in which a fibrous web based oncellulosic fibers is sandwiched between two webs of continuousfilaments, which method consists:

[0019] in producing a first web of continuous filaments, the bundle ofextruded and drawn continuous filaments being taken up on a movingconveyor belt in the form of a nonbonded lap;

[0020] in depositing on this web, by the airlaid technique, a second webof cellulosic fibers;

[0021] in depositing on the fibrous web a second web of nonbondedcontinuous filaments;

[0022] in transferring the complex formed onto a water-jet bonding unitand in consolidating the assembly by hydro-entanglement; and

[0023] in drying the hybrid nonwoven produced and then taking it up, forexample in the form of a wound package.

[0024] According to a preferred way of implementing the method accordingto the invention, the cellulosic fibers used in the production of thecomplex are wood fibers and they are deposited by pneumatic layering.

[0025] Moreover, if it is conceivable to carry out only a singlewater-jet bonding treatment, the complex formed is preferably subjectedto two successive treatments acting against the two opposed sides of thecomplex.

[0026] The invention also relates to a novel type of nonwoven productobtained by implementing this method.

[0027] Such a hybrid nonwoven, which therefore consists of a mixture offibers of different type, is characterized in that it is composed of aply of natural fibers, especially wood fibers, trapped between twononwoven webs consisting of extruded and drawn filaments, based on asynthetic material, the cohesion of the various plies being obtained byentanglement thanks to the action of water jets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention and the advantages which stem therefrom will,however, be more clearly understood from the illustrative examples whichfollow, given below by way of indication but implying no limitation, andwhich are illustrated by the appended drawings in which:

[0029]FIG. 1 is a schematic view of an entire line for producing acomplex fabric produced in accordance with the method according to theinvention; and

[0030]FIGS. 1a, 1 b, 1 c and 1 d are enlarged views of the regionscircled in this FIG. 1.

MANNER OF REALIZING THE INVENTION

[0031] A composite nonwoven is produced continuously on a productionline, like that illustrated in FIG. 1.

[0032] To do this, a first web (2) of continuous filaments is producedby means of a production unit, denoted by the general reference (1), bymelting, spinning and drawing, which filaments are deposited anddistributed over a moving conveyor belt (3).

[0033] Optionally, immediately after formation, this first web (2) maybe subjected to a compacting operation by means of a press roll or bythe action of jets coming from a rail of water injectors.

[0034] The continuous filaments of this first web (2) may be based on apolymer consisting of polypropylene, polyester or other syntheticmaterials, such as a polyethylene or polyamide, this list not beingexhaustive. Optionally, the continuous filaments may consist of what arecalled “bicomponent” filaments, such as those obtained by thecoextrusion of polypropylene and polyethylene.

[0035] The web (2) of nonbonded continuous filaments is then transferredunder a unit, denoted by the general reference (4), which, by theairlaid technique, allows discontinuous fibers (4), of another type, andmore particularly cellulosic, especially wood, fibers, to be depositedon the surface of the first web (2).

[0036] The cellulosic fibers are deposited on the surface of the firstweb (2) by means of a stream of air. Preferably, the filamentary web (2)is held in place on the conveyor belt (3) by means of a suction unit(5). Thereafter, said fibers (4) are preferably deposited between thenonbonded filaments of the web (2) by the effect of the suction, thusallowing excellent integration of the two constituents.

[0037] The complex (2, 4) which is still held in place supported by theconveyor belt (3) is then taken under a second zone (6) for forming asecond web (7) of continuous filaments, these also being syntheticfilaments, of the same type as or of a different type from those of thefirst web (2).

[0038] A press roll (8) is preferably placed after this zone fordepositing the web (7) and makes it possible to compact the assembly forthe purpose of transferring it to the water-jet bonding unit, denoted bythe genera; reference (9), which follows the production line.

[0039] Optionally, this compacting operation could be carried out bymeans of a rail of water injectors.

[0040] The complex is then introduced into the water-bonding zone (9) ona conveyor (10) on which are carried out, in succession, the operationsof compacting and prewetting the assembly by means of an upper conveyor(11) tangential to the lower conveyor (10), and within which a waterinjector (12) is placed.

[0041] After the complex has been compacted and prewetted, it issubjected to the action of a succession of water jets (13) delivered byseveral water injectors placed in series.

[0042] These water jets (13) consolidate the assembly consisting of thevarious plies of the complex and give the upper ply good abrasionresistance.

[0043] The structure thus treated is then transferred, by being turnedupside down, onto a cylinder (14), or onto another conveyor, associatedwith several injectors (15) which also deliver water jets onto the otherside of the complex, thus reinforcing the consolidation of the assemblyof plies, while giving the ply facing the jets good abrasion resistance.

[0044] The complex thus obtained is then transferred onto an expressingconveyor (16) on which it is expressed by means of a suction boxconnected to a vacuum generator.

[0045] It is then dried by means of a traversing air cylinder (17) andthen taken up in a conventional manner, for example in the form of awound package (18).

EXAMPLE

[0046] A product in accordance with the invention is produced in thefollowing way.

[0047] A web (2) of continuous filaments, weighing 15 g/m², is producedon a unit sold by the Applicant under the name “spunjet”, which allows anonwoven web to be produced by extrusion, drawing and distribution ofcontinuous filaments.

[0048] In this embodiment, as polymer, polypropylene such as that soldby Amoco under the reference 100 ZA 35 is extruded.

[0049] The web formed consists of 7000 filaments per meter of width andis produced at a rate of 250 meters per minute. The diameter of thefilaments after drawing is about 15 microns.

[0050] A suction unit placed opposite the drawing slit (20) allowsprecise control of the way in which the filament is deposited on theconveyor belt (3) and of its uniformity thereover.

[0051] Placed above the same conveyor (3) is a unit (4) fordistributing, by the airlaid technique, discontinuous fibers over theweb (2) formed beforehand.

[0052] Such a fiber-distributing unit may consist of a conventional unitsuch as that sold by M & J.

[0053] In the specific example, 35 g/m² of cellulosic fibers, and moreparticularly wood fibers, sold by Korsnaes, were deposited on thespunbond web (2), these wood fibers, with a length of around 3 mm, beingusually referred to by the expression “fluff pulp”.

[0054] A suction box (5) is placed beneath the conveyor under the entiresurface of the airlaid distributing head (4). This suction head (5) isconnected to a vacuum generator which allows the wood fibers to beuniformly distributed while maintaining the homogeneity of the spunbondweb (2).

[0055] A press roll (not shown), the speed of which is synchronized withsaid belt (3), compacts the assembly thus formed.

[0056] After compacting, a second spunbond web, weighing 15 g/m², of thesame type as the first web (2) is deposited on the surface of thecomplex.

[0057] This second web may be formed either on the same conveyor (3) oron a separate conveyor.

[0058] This web (7) is therefore distributed over the ply (4) ofcellulosic fibers. Preferably, transfer takes place in a positive mannerusing a suction box (5 a) placed beneath the main conveyor opposite thepoint of transfer.

[0059] The structure obtained, which weighs 65 g/m², is optionallycompacted by means of a roller (8). This compacting may optionally becarried out by means of an additional rail of water injectors.

[0060] The complex is then transferred onto the conveyor (10) of thewater-jet bonding unit (9).

[0061] Such a bonding unit comprises a main conveyor (10) above which isplaced an upper conveyor (11) tangential to the latter, and inside whichis placed a water injector (12) delivering 4000 jets of water per meter,these jets having a diameter of 130 microns and a velocity of 34 metersper second.

[0062] The sandwich thus compacted and wetted is treated on its topsideby six water injectors (13), placed in series, which blast water jets120 microns in diameter spaced apart by 0.6 mm with velocities of 110,125, 140, 140, 140 and 140 m/s respectively.

[0063] The treated complex is then transferred, by turning it over, ontoa cylinder (14) around which are placed four water injectors (15) whichblast water jets 120 microns in diameter spaced apart by 0.6 mm withvelocities of 125, 140, 140 and 140 m/s, respectively.

[0064] The complex thus consolidated is transferred onto an expressingconveyor (16), on which it is expressed by a suction box in which thereis a vacuum of 400 mbar.

[0065] The assembly is then dried at a temperature of 120° C. by atraversing air cylinder (17), and then taken up at (18).

[0066] It is observed that the product obtained at the end of theproduction line weighs about 60 g/m², exhibits excellent homogeneity,has a good handle and great pliancy, and excellent abrasion resistanceboth in the dry state and in the wet state.

[0067] It has a high water absorptivity, of around 850%.

[0068] Such a water absorptivity is comparable to that of hybridnonwovens consisting of discontinuous fibers and produced by carding.

[0069] On the other hand, the abrasion resistance both in the dry stateand in the wet state, together with the mechanical properties, aregreatly superior.

[0070] Such a product is perfectly adapted to various applications, suchas industrial or domestic wiping products, impregnated wipes andoperating gowns and drapes, such applications being given by way ofindication, but implying no limitation.

1. A method for producing a complex nonwoven fabric which consists incontinuously producing a complex in which a fibrous web (4) based oncellulosic fibers is sandwiched between two webs (2, 7) of continuousfilaments, which method consists: in producing a first web (2) ofcontinuous filaments, the bundle of extruded and drawn continuousfilaments being received on a moving conveyor belt (3) in the form of anonbonded lap; in depositing on this web (2), by the airlaid technique,a second web (4) of cellulosic fibers; in depositing on the fibrous web(4) a second web (7) of nonbonded continuous filaments; in transferringthe complex thus formed onto a water-jet bonding unit (9) and inconsolidating the assembly by hydro-entanglement; and in drying thehybrid nonwoven produced and then taking it up, for example in the formof a wound package (18).
 2. The method as claimed in claim 1,characterized in that the cellulosic fibers (4) used in the productionof the complex are wood fibers.
 3. The method as claimed in either ofclaims 1 and 2, characterized in that the complex is subjected to twosuccessive bonding treatments by water jets acting against the twoopposed sides of said complex.
 4. A hybrid nonwoven obtained byimplementing the method as claimed in one of claims 1 to 3,characterized in that it is composed of a ply (4) of natural fibers,especially wood fibers, trapped between two nonwoven webs (2, 7)consisting of continuous, extruded and drawn filaments, based on asynthetic material, the cohesion of the various plies being obtained byentanglement thanks to the action of water jets.